The In-situ Experiment Of Inefficient Fracturing Prevention For Polymer-flooding Producer

The article was based on the on-site supervision and the multidisciplinary analysis before and after the fracturing for inefficient polymer-flooding producers, it was apt that reservoir of higher permeability and lower pressure was inefficient after the facturing. Fracturing fluid, by the mechanism analysis of facturing would leak off after entering into the rock matrix during operation, some polymer, such as guanidine gel, would be filterd out and stayed in low-permeability rock surface to form mud cake, the permeability of which was generally much lower than that of strata. Indoor study have shown that there were two different forms which were caused by hydraulic fracturing: internal damage of crack itself(filling injury of proppant)and penetrating injury to formation of crack (surface damage of crack), both of which were major injury factors in the high-permeability reservoir. As exploitation of polymer-flooding was concerned, the main productive zone and selective zone for fracturing were both high-permeability reservoirs, polymer and additives in the fracturing fluid were able to penetrate most of the pore throats and formed mud cake. In this case, Internal anti-filtration resistance of rock declined significantly. Therefore, the differential pressure which was needed to recover permeability before fracturing or enhance its conductivity in the vicinity of crack should exceed the start pressure, otherwise, it would result in no-liquid production of selective zone after fracturing , which was namely that there was no any production at all in the whole well. But as waterflooding exploitation to be concernd, fracturing layers were merely as part of an oiler's production intervals and of relatively low permeability, they would not affect other production pays that they were unable to result in no-production in the whole well even if the pressure of selective zones to fracture was so low that fracturing liquid stayed in the formation. Based on the above analysis, we examined and distinguished polymer-flooding producers, according to the correlative value between the front end of crack seam and threshold pressure gradient, which were suitable for fracturing by laboratory experiment and theoretical investigation.